DEVELOPMENT OF A COGNITIVE TESTING APPARATUS FOR SOCIALLY HOUSED MOTHER-PEER-REARED INFANT RHESUS MONKEYS

Although the cognitive development of nursery-reared (NR) infant monkeys is well described, nothing is known about the typical development of mother-peer-reared (MPR) infants. We developed a cognitive testing apparatus for socially-housed, MPR infant rhesus macaques (Macaca mulatta, n=5) that allowed infants to freely return to their mothers for contact comfort as needed, and compared their training and performance on an object detour reach (ODR) task to that of NR infants (n=11), which were tested in their home cages via a cage-side apparatus. MPR and NR infants did not differ on the number of days or sessions to reach criterion for training, indicating the MPR infants’ comfort and willingness to engage in and learn the task. Performance on the task differed between rearing groups: overall, MPR infants balked more (U=533.0, p<0.001), got fewer trials correct (U=1230.0, p<0.001), and took longer to complete trials (U=549.5, p=0.012) than NR infants. However, further analysis revealed that these differences existed only in the first 1-2 days of testing and then disappeared, suggesting that MPR infants are likely initially performing more poorly than NR infants due to their lack of intensive experience with human experimenters. These are the first cognitive data in freely-performing MPR rhesus monkeys under <1 year, and they underscore the utility of our apparatus for comparing cognitive development in a normative population of infant monkeys to other populations.